Conducting polmers

It's about Conducting Polymers their history and the latest discovery in the field with their application. And the future scope of the conducting Polymer. Here you will find all in one place.

1. CONDUCTING POLYMERS Amit Soni Int. Ph.D 2 nd Year S0626

2. Polymers are long chain like molecular structure where repeated molecular units are connected by covalent bonds Polymers (or plastics as they are also called) are known to have good insulating properties.  Polymers are one of the most used materials in the modern world.Their uses and application range from containers to clothing. They are used to coat metal wires to prevent electric shocks.  Introduction:

3. Through simple modification of ordinary organic conjugated polymers, the attributes of electrical conduction, can be coupled with material-based properties of polymers, leading to the formation of Conductive Polymers How can be these polymers are conducting??

4. History: Discovered in the late seventies (1977) by Alan Heegar , Alan Macdiarmid and Dr. Hideki Shirakawa. Before that polymers were used as insulators in the electronic industry Advantages over conductors Chemical - ion transport possible , redox behaviour , catalytic properties, electrochemical effects, Photo-activity, Junction effects Mechanical - light weight , flexible , non metallic surface properties

5. What is conductivity? Conductivity can be defined simply by Ohms Law. V= IR Where R is the resistance , I the current and V the voltage present in the material. The conductivity depends on the number of charge carriers (number of electrons) in the material and their mobility.In a metal it is assumed that all the outer electrons are free to carry charge and the  impedance to flow of charge is mainly due to the electrons "bumping" in to each other.  Insulators however have tightly bound electrons so that nearly no electron flow occurs so they offer high resistance to charge flow.  So for conductance free electrons are needed.

6. What makes the material conductive? Three simple carbon compounds are diamond, graphite and polyacetylene. They may be regarded as three- two- and one-dimensional forms of carbon material s . Diamond, which contains only σ bonds, is an insulator and its high symmetry gives it isotropic properties. Graphite and acetylene both have mobile π electrons and are, when doped, highly anisotropic metallic conductors.

7. How can plastic become conductive? Plastics are polymers , molecules that form long chains, repeating themselves. In becoming electrically conductive, a polymer has to imitate a metal, i.e., its electrons need to be free to move and not bound to the atoms. Polyacetylene is the simplest possible conjugated polymer. It is obtained by polymerisation of acetylene.

8. Two conditions to become conductive : 1.The first condition for this is that the polymer consists of alternating single and double bonds, called conjugated double bonds. . 2. The second condition is that the plastic has to be disturbed - either by removing electrons from (oxidation), or inserting them into (reduction), the material. i.e., by Doping. 1-oxidation with halogen ( p- type). 2- Reduction with alkali metal ( n -type).

9. Comparison of conductivity: Most of these polymers are semiconducting in nature.

10. Doping process: The halogen doping transforms polyacetylene to a good conductor. Oxidation with iodine causes the electrons to be jerked out of the polymer, leaving "holes" in the form of positive charges that can move along the chain. The lonely electron of the double bond, from which an electron was removed, can move easily. As a consequence, the double bond successively moves along the molecule. The positive charge, on the other hand, is fixed by electrostatic attraction to the iodide ion, which does not move so readily.

11. 2 Photodoping : Irradiation of a conjugated polymer with a light beam of energy greater than its band gap could promote electrons from the valence band into the conduction band Although the photogenerated charge carriers may disappear once the irradiation ceases, the application of an appropriate potential during irradiation could separate electrons from holes, leading to photoconductivity. 3 Charge Injection Doping : Charge carriers can be injected into the band gap of conjugated polymers by applying an appropriate potential on the metal/insulator/polymer multilayer structure.

12. Understanding the terms: Polarons : Unipositive or Uninegative Charge Carriers. Spin= 1/2 Biplarons : Dipositive or Dinegative. Coupled from 2 polarons. Spin = 0 Solitons : Unpaired π electrons, resembling charge on free radicals. Spin = ½ for neutral and 0 for +ve/ -ve From Su- Schrieffer- Heeger (SSH) Model These are quantum particles that are responsible for conductivity

13. Propagation of Polaron: Polaron can be thought as a Bound state of a charged & neutral soliton whose mid-gap energy states hybridize to form bonding and anti-bonding levels. Energy Level Diagram  

14. A Bipolar is a bound state of two charged solitons of like charge with two corresponding mid-gap levels. example: Polythiophene Propagation of Bipolaron:

15. Solitons are responsible for higher conductivity Double bond next to a soliton may switch over to give rise a moving soliton which leads to conduction In presence of many soliton, their sphere of influence overlaps leading to conduction like metals.

16. A Soliton is a mobile charged or neutral defect, propagating along the chain to reduce the interconversion barrier. Propagation of Solitons R and L forms are interconverted through a charge carrier soliton. Soliton is a mobile, charged or neutral defect or a kink in the polymer chain Propagated down the polymer chain. It is a non-bonding state.

17. Factors that affect the conductivity: 1.Density of charge carriers. 2.Their mobility. 3.The direction. 4. Presence of doping materials (additives that facilitate the polymer conductivity) 5. Temperature.

18. The conductivity of conductive polymers decreases with falling temperature in contrast to the conductivities of typical metals, e.g. silver, which increase with falling temperature . Effect of Temperature: For 3-D system: T 3d = c/k B N(E f )L 3 c = constant k B = Boltzmann constant N(E f ) = number density at the Fermi Level L = localisation length (effective conjugated chain length)

19. Polarons and bipolarons give rise to temperature-independent paramagnetic susceptibility, apart from the temperature dependent Curie susceptibility. Experimental χ spin can be resolved into Pauli and Curie contributions according to the expression χ spin = χ p + C/T where C is Curie constant and χ p is Pauli susceptibility expressed as χ p = μ B 2 N(E f ) Magnetic Properties:

20. Photographic Film smart" windows Shield for computer screen against electromagnetic "smart" windows radiation Light-emitting diodes Solar cell Various Applications

21. Coatings: Prevents buildup of static charge in insulators Absorbs the harmful radiation from electrical appliances which are harmful to the nearby appliances Polymerisation of conducting plastics used in circuit boards

22. Sensors(to gases and solns.) • Polypyrroles can detect NO2 and NH3 gases by changing its conductivity • Biosensor : polymerization of polyacetylene in presence of enzyme glucose oxidase and suitable redox mediator like triiodide will give rise to a polymer which acts as glucose sensor

23. Polymeric Ferroelectric RAM(PFRAM): Uses polymer ferroelectric material • Dipole is used to store data • Provides low cost per bit with high chip capacity • Low power consumption • No power required in stand by mode • Isn’t a fast access memory

24. Biocompatible Polymers: Artificial nerves Brain cells

25. Batteries: • Light weight • Rechargeable • Example - Polypyrrole - Li & Polyaniline - Li 3.7V, 30-10000 mAh

26. Conductive Adhesive: Monomers are placed between two conducting plates and it allows it to polymerise. Conducting objects can be stuck together yet allowing electric current to pass through the bonds.

27. Current Status

28. Problem areas: Reproducibility. Stability. Difficulty to process. Short life span. High cost. Difficult to fabricate in labs.

29. References: 1.H. Shirakawa, E.J. Louis, A.G. MacDiarmid, C.K. Chiang and A.J. Heeger, J Chem Soc Chem Comm (1977) 579 2.T. Ito, H. Shirakawa and S. Ikeda, J.Polym.Sci.,Polym.Chem. Ed. 12 (1974) 11–20 3.C.K. Chiang, C.R. Fischer, Y.W. Park, A.J. Heeger, H. Shirakawa, E.J. Louis, S.C. Gau and A.G. MacDiarmid , Phys. Rev. Letters 39 (1977) 1098 4.C.K. Chiang, M.A. Druy, S.C. Gau, A.J. Heeger, E.J. Louis, A.G. MacDiarmid*, Y.W. Park and H. Shirakawa, J. Am. Chem. Soc. 100 (1978) 1013 5.Evaristo Riande and Ricardo Díaz-Calleja, Electrical Properties of Polymers 6.http://nobelprize.org/nobel_prizes/chemistry/laureates/2000/index.html http://www.organicsemiconductors.com . 7.Solitons in Polyacetylene: Effects of Dilute Doping on Optical Absorption Spectra (N. Suzuki, M. Ozaki, S. Etemad, A. J. Heeger, and A. G. MacDiarmid) , Phys Rev Lett, 45, 1209 8. Electrical Conductivity in Doped Polyacetylene (C. K. Chiang, C. B. Fincher, Jr., Y. W. Park, and A. J. Heeger; H. Shirakawa, E.J. Louis, S. C. Gau, and Alan G. MacDiarmid ) , Phys Rev Lett, 39, 1098 9.Solitons in Polyacetylene: Magnetic Susceptibility (S. Ikehata, J. Kaufer, T. Woerner, A. Pron, M. A. Druy A. Sivak, A. J. Heeger, and A. G. MacDiarmid ) Phys Rev Lett, 45, 1123

30. Thank You..!!!